The present invention relates to pumpable refractory compositions and, more particularly, to a pumpable ceramic fiber composition resistant to deterioration under repeated freezing and thawing cycles.
Various lightweight, insulating ceramic fiber refractory compositions are available in pre-formed shapes, blankets, bricks and panels. These materials are frequently used in furnace interiors because of their light weight which reduces heat storage and, therefore, conserves fuel and reduces furnace heat-up time. Unfortunately, the use of such refractory compositions is limited to relatively simple shapes and to applications such as lining industrial furnaces and the like. To compliment such formed ceramic fiber refractory products of definite dimensions, pumpable insulating refractory compositions comprising ceramic fiber, an aqueous binder system, and a liquid vehicle carrier have been developed. Such pumpable insulating refractory compositions are formed into the desired shape in-place in the desired location. The liquid vehicle carrier is then evaporated from the pumpable refractory composition with heated air so as to set the refractory composition in its final shape.
Because such pumpable ceramic fiber compositions must remain pumpable until such time as a customer intends to use it, such ceramic fiber compositions are shipped and stored in air-tight and water-tight containers. However, during shipping and storage such pumpable refractory fiber compositions are often subjected to sufficiently low temperatures such that freezing of the aqueous portion of the composition may occur. In fact, such compositions are often subjected to repeated cycles of freezing and thawing during shipping and storage.
In many conventional prior art pumpable ceramic fiber compositions, colloidal silica comprises the binder system. For example, U.S. Pat. Nos. 4,040,847; 4,174,331; and 4,248,752 each discloses a moldable ceramic fiber composition comprised of ceramic fiber with water as a liquid vehicle and colloidal silica as the binding system. In such prior art compositions containing colloidal silica as the binding system and water as the liquid vehicle carrier, subjecting the pumpable ceramic fiber composition to freezing has caused the colloidal silica to precipitate out of the system and the fiber mix, thereby, substantially deteriorating the product. In the aforementioned U.S. Pat. No. 4,040,847, the problem of deterioration of the colloidal silica binder system as a result of freezing is addressed. The solution proposed therein is to add ethylene glycol to the colloidal silica binder.
Accordingly, it is an object of the present invention to provide a pumpable ceramic fiber mixture which incorporates a binder which is resistant to deterioration under repeated freezing and thawing cycles and does not include ethylene glycol thereby, avoiding potential health hazards associated with ethylene glycol.
Additionally, it is a further object of the present invention to provide such a stable pumpable ceramic fiber composition which has good pumpability, high insulating value, high strength, good resistance to shrinkage at elevated temperatures, and which may be installed in a cold or hot operating boiler or furnace wall.